Thank you for affing back autofill of extensions:
" When exporting a file, the file extension is now always added (except for custom FFmpeg and external program exports)."
But there is still a problem with it. Pre 3.4, you could simply hit RETURN and it would do the export since Export Audio was the default for the window. In 3.41 you can still hit return to export the audio, but when you do, it doesn’t perform the autofill of extension you just added (wav, mp3, etc)